diff --git a/core/lib/Drupal/Core/EventSubscriber/ExceptionTestSiteSubscriber.php b/core/lib/Drupal/Core/EventSubscriber/ExceptionTestSiteSubscriber.php
index 8954af8..6e4f82d 100644
--- a/core/lib/Drupal/Core/EventSubscriber/ExceptionTestSiteSubscriber.php
+++ b/core/lib/Drupal/Core/EventSubscriber/ExceptionTestSiteSubscriber.php
@@ -75,7 +75,7 @@ public function on500(GetResponseForExceptionEvent $event) {
   public function onResponse(FilterResponseEvent $event) {
     if ($this->canAddHeaders()) {
       $response = $event->getResponse();
-      $memory_usage = memory_get_usage();
+      $memory_usage = memory_get_peak_usage(TRUE);
       $response->headers->add([
         'X-Drupal-Memory-Peak' => round($memory_usage / 1024 / 1024, 2),
       ]);